Airbag with controlled venting

Abstract

An airbag is formed of two or more panels with one or more panel being impervious and the second being pervious to gases. A layer is attached to the gas permeable panel and has a dimension selected to insure that the airbag has a preselected maximum peak pressure during deployment.

We claim: 
     
       1. An airbag for a vehicular occupant restraint system comprising: a circular first panel made of a material impervious to gases;   a circular second panel attached to said first panel to form a bag, said second panel having an opening for receiving an inflator and being made of a single fabric; and   a protective layer attached to said second panel and disposed about said opening, said protective layer having a dimension selected to limit the peak pressure within said bag to a preselected range when such bag is inflated for the protection of an occupant;   said second panel being made of a material pervious to gases and said protective layer being made of a material impervious to said gases;   for the same size of said panels, said protective layer being so constructed, dimensioned and arranged to be larger in size for a smaller inflator and smaller in size for a larger inflator in order to produce the required peak pressure within the bag at the moment the occupant hits the inflated bag.   
     
     
       2. The airbag of claim wherein said preselected peak pressure is in the range of 0.1-10 PSI. 
     
     
       3. The airbag of claim 1 further comprising a second layer, said second layer cooperating with said first layer to sandwich an portion of said second panel therebetween. 
     
     
       4. The airbag of claim 3 wherein said second layer has the same linear dimension as said first layer. 
     
     
       5. The airbag of claim 3 wherein said first layer and said second layer are attached to each other, with said portion being disposed therebetween. 
     
     
       6. The airbag of claim 3 wherein said second layer is disposed inside said bag and is provided with a plurality of integral straps, said straps forming tethers for said airbag. 
     
     
       7. The airbag of claim 6 further comprising a third layer disposed inside said bag and attached to said first panel, said straps being secured to said third layer. 
     
     
       8. A method of making a plurality of airbags comprising the steps of: forming a first and a second panel, said first panel being made of a gas impervious material, said second panel being made of a gas pervious material and having an access hole for receiving an inflator;   forming a first reinforcing layer and protective second layer of a gas impervious material, said second layer being disposed inside said bag;   attaching said panels and said layers to form a bag, said panels being peripherally attached and said first and second layers being attached to said second panel to render a portion of said second panel gas impervious, said layers having a linear dimension selected to define a preselected peak gas pressure;   for the same size of said panels, said protective layer being so constructed, dimensioned and arranged to be larger in size for a smaller inflator and smaller in size for a larger inflator in order to produce the required peak pressure within the bag at the moment the occupant hits the inflated bag.   
     
     
       9. The method of claim 8 wherein said first layer is substantially circular and said second layer being formed with a plurality of straps extending radially, attaching said straps to said first panel to form tethers. 
     
     
       10. The method of claim, 9 wherein said straps are integrally formed with said second layer. 
     
     
       11. The airbag of claim 8 wherein said second layer is superimposed over said second panel and is made of fire resistant material for protecting said bag from hot gases.